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Alpha-Fetoprotein (AFP) in Blood

Test Overview

An alpha-fetoprotein (AFP) blood
test checks the level of AFP in a pregnant woman's blood. AFP is a substance
made in the liver of an unborn baby (fetus). The
amount of AFP in the blood of a pregnant woman can help see whether the baby
may have such problems as
spina bifida and
anencephaly. An AFP test can also be done as part of a
screening test to find other
chromosomal problems, such as
Down syndrome (trisomy 21) or
Edwards syndrome (trisomy 18). An AFP test can help
find an omphalocele, a congenital problem in which some of the baby's
intestines stick out through the belly wall.

Normally, low levels
of AFP can be found in the blood of a pregnant woman. No AFP (or only a very
low level) is generally found in the blood of healthy men or healthy,
nonpregnant women.

The level of AFP in the blood is used in a
maternal serum triple or quadruple screening test.
Generally done between 15 and 20 weeks, these tests check the levels of three
or four substances in a pregnant woman's blood. The triple screen checks
alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and a type of
estrogen (unconjugated estriol, or uE3). The quad screen checks these
substances and the level of the hormone inhibin A. The levels of these
substances—along with a woman's age and other factors—help the doctor estimate
the chance that the baby may have certain problems or birth defects.

Screening tests are used to see what the chance is that your baby has a
certain birth defect. If a screening test is positive, it means that your baby
is more likely to have that birth defect and your doctor may want you to have a
diagnostic test to make sure.

Men, nonpregnant women, and children

In men,
nonpregnant women, and children, AFP in the blood can mean that certain types of
cancer—especially cancer of the
testicles,
ovaries, stomach,
pancreas, or liver—are present. High levels of AFP may
also be found in
Hodgkin's disease,
lymphoma, brain tumors, and renal cell cancer.

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Why It Is Done

The AFP test is done to:

Check the developing baby (fetus) of a pregnant woman for
brain or spinal problems (called
neural tube defects). Such defects occur in about 2
out of every 1,000 pregnancies.footnote 1 The chance of a
neural tube defect in a baby is not related to the mother's age. Most women
whose babies have neural tube defects have no family history of these problems.

Check the developing baby (fetus) of a pregnant woman for Down syndrome.

Find certain cancers, especially cancer of the
testicles, ovaries, or liver. But up to half of the people with liver cancer do
not have high AFP levels.

How To Prepare

You do not need to do anything before
you have this test.

If you are pregnant, you will be weighed
before the blood test, because the test results will be based on your weight.
The test results are also based on race, age, and how many weeks you are in your
pregnancy.

How It Is Done

The health professional drawing blood
will:

Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.

Clean the needle site with
alcohol.

Put the needle into the vein. More than one needle stick
may be needed.

Attach a tube to the needle to fill it with
blood.

Remove the band from your arm when enough blood is
collected.

Put a gauze pad or cotton ball over the needle site as
the needle is removed.

Put pressure on the site and then a
bandage.

How It Feels

The blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight.
You may feel nothing at all from the needle, or you may feel a quick sting or
pinch.

You may feel anxious while awaiting results of an
alpha-fetoprotein test done to determine the health of your unborn baby.

Risks

There is very little chance of a problem from
having blood sample taken from a vein.

You may get a small bruise at the site. You can lower the chance
of bruising by keeping pressure on the site for several minutes.

In
rare cases, the vein may become swollen after the blood sample is taken. This
problem is called phlebitis. A warm compress can be used several times a day to
treat this.

Results

An alpha-fetoprotein (AFP) blood test
checks the level of AFP in a pregnant woman's blood. AFP is a substance made in
the liver of a developing baby (fetus). The amount of AFP in the blood
of a pregnant woman can help find certain problems with her baby.

Normal

The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, normal values vary with the age of the baby. A high or low AFP may mean
that the age of the baby has been recorded wrong or not calculated correctly.
An
ultrasound may be done to check the baby's age more
accurately.

In pregnant women, the amount of AFP gradually rises
starting in the 14th week of pregnancy. It continues to rise until a month or
two before giving birth, then it slowly decreases. Values are generally
slightly higher for black women than they are for white women. Values are
slightly lower for Asian women than they are for white women. An accurate
estimate of the age of the baby is needed to understand the AFP value
correctly.

The normal range of AFP values is adjusted for each
woman's age, weight, and race; whether she has
diabetes that needs injections of
insulin; and the age of her baby (gestational age). If
the age of the baby is changed after an ultrasound, the AFP must then be
adjusted as well. Each woman and her doctor need to look at the range of
AFP values that is normal for her when she has an AFP test.

High values

In a pregnant woman, high alpha-fetoprotein values can mean:

The age (gestational age) of the baby is
wrong.

The woman is pregnant with more than one baby, such as twins
or triplets.

The baby has a neural tube defect.

The
baby's intestines or other abdominal organs are outside the body (called an
abdominal wall defect or omphalocele). Surgery after birth will be needed to
correct the problem.

What To Think About

AFP is a screening
test to look for possible problems in your developing baby.
Other tests will likely be done if the AFP results are abnormal. An ultrasound will likely be done if the AFP is abnormal. If an ultrasound cannot find the
cause of the abnormal AFP, an amniocentesis may be recommended.

A normal AFP result does not guarantee a normal pregnancy or
healthy baby.

The amount of AFP in the amniotic fluid may also be
measured using
amniocentesis. Most women have normal AFP levels in
the amniotic fluid, even though the levels may be abnormal in their blood.
These women are at low risk of having a fetus with a neural tube defect.

If abnormal levels of AFP
are found, talk with your doctor or a
genetic counselor. AFP test results can be abnormal,
even when nothing is wrong with the baby.

In people with liver
cancer or other types of cancer, a decrease in AFP may mean treatment is
working.

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